Comparison of mass discrimination correction methods and sample introduction systems for the determination of lead isotopic composition using a multicollector inductively coupled plasma mass spectrometer.
The influence of sample introduction system on Neptune MC-ICPMS lead isotopic ratio measurements was tested on dilute solutions of the lead certified material NIST SRM 981 ([Pb] = 0.2-170 ng g(-1)) using (1) a SIS spray chamber, (2) a MCN 6000 desolvating system, or (3) an Apex inlet system. The impact of using a high-efficiency X-cone in place of a standard H-cone with the MCN and Apex was also investigated. Performance of the sample introduction systems varied with lead concentration. Over 10 ng g(-1), no system was significantly more precise or accurate. As lead concentrations decreased, both accuracy and precision diminished, and below 1 ng g(-1), use of an X-cone in combination with the Apex and particularly with the MCN system notably improved the quality of the measurements. Various mathematical methods of mass bias correction using thallium additions were tested. Selection of (205)Tl/(203)Tl for NIST SRM 997 to optimize data (1) daily, (2) for each introduction system, and (3) over all sessions significantly improved the data, with no major difference in the output between the three methods. Consistency of the (205)Tl/(203)Tl ratio (2.3888) optimized over all data with previous observations by others supports the use of this value for future measurements.
Gallon
Céline
C
Environmental Toxicology Department, University of California Santa Cruz, Santa Cruz, California 95064, USA. gallon@etox.ucsc.edu
Aggarwal
Jugdeep
J
Flegal
A Russell
AR